Automatic A/c-Heater System: Other Land Rover Discovery II

AUTO Mode

In AUTO mode, air distribution and blower speeds are adjusted automatically to achieve and then maintain desired temperature. Control panel display will show AUTO together with air distribution and blower speed settings. (Scheme 13) Both air distribution and blower controls can be operated independently to override automatic setting. When air distribution and blower speed has been manually changed, symbols will move outside enclosed area in center of display indicating that they are no longer being controlled automatically.

Scheme 13

Temperature Control

Note. Temperatures shown on control panel display are target temperatures only and are not specific temperature measured within vehicle interior.

Operate either driver's or passenger's temperature control switch to set desired temperature for corresponding side of passenger compartment. Temperatures that are more than 82°F (28°C) and less than 61°F (16°C) cannot be set. When attempted, temperatures set above or below these maximum and minimum settings will cause HI or LO to appear in control panel display. A/C system will not achieve passenger's side temperatures that are more than 9°F (5°C) greater or less than temperatures set for driver's side.

To determine amount of heating or cooling required, ATC ECU uses sensor inputs and temperatures selected on control panel to calculate target air outlet temperatures for driver's and front passenger's side of heater assembly. ATC ECU then signals actuator motors controlling respective blend flaps in heater assembly to move flaps to appropriate position. Target temperatures are constantly updated and, in automatic mode, also used in further calculations to determine inlet air source, blower speed and air distribution.

Defrost Mode

If windshield is misting or covered in ice, press the defrost mode button. System will immediately direct output to achieve maximum windshield clearing. A/C system will set blower speed to maximum and distribute airflow to windshield only. In addition, rear window and front windshield heaters (if equipped) will be turned on, or timed operating cycle will start over if they are already activated. Temperature and blower speed controls can be adjusted and air recirculation selected manually if desired. When defrost mode button is pressed a second time or AUTO button is select A/C system will exit defrost mode and default automatically to AUTO mode.

ECON Mode

In economy mode, A/C compressor is turned off and system functions as a conventional heating and ventilation system. This reduces engine load and reduces fuel consumption. Select economy mode whenever A/C is not required, as in cold weather, when external temperature is less than required temperature for passenger compartment. Air distribution, blower speed and recirculation controls can be operated independently. Pressing economy mode button a second time will activate A/C compressor and return system to AUTO mode. In economy mode, blower off can be turned off with no segments showing in control panel display.

Blower Speed

Press blower button to adjust blower speed. Blower speed increases incrementally with each press of blower button. When maximum blower speed is reached, control panel display will show MAX and 5 segments. When maximum blower speed has been reached, pressing button again will return blower to slowest speed and one segment shows.

Air Distribution Control

Air distribution changes in order with each press of air distribution control button as follows

1. Face level vents.
2. Foot and face level vents.
3. Foot level vents.
4. Foot level, windshield and side window vents.
5. Windshield and side window vents.

On the next operation of air distribution button, air distribution returns to beginning of sequence. If button is pressed for more than one second, air distribution will automatically default to foot and face level vents. A specific air distribution symbol will be shown on control panel display for selected distribution.

External Temperature

When external temperature button is pressed external temperature is displayed for approximately 6 seconds, after which control panel display returns to previous display. When A/C system is turned off, external temperature can be displayed briefly by pressing external temperature button.

Air Recirculation

Air recirculation feature can be used to keep outside air from entering vehicle and recirculating air inside vehicle. This is useful for preventing entry of undesirable fumes. Air recirculation can significantly influence dehumidifying and cooling performance of A/C system. In AUTO mode, air recirculation is controlled automatically to enable A/C system to achieve its optimum performance.

Air recirculation can be manually selected in AUTO, defrost and economy modes. In AUTO mode, press air recirculation button briefly (display shows recirculation symbol). Air recirculation operates until button is pressed a second time to turn air recirculation off. If air recirculation button is pressed and held for 2 seconds (2 beeps will sound and display shows recirculation symbol), air recirculation will operate for a timed period of 4-6 minutes. In defrost and economy modes, press air recirculation button briefly (display shows recirculation symbol). Air recirculation will operate for a timed period of 4-6 minutes. If air recirculation button is pressed and held for 2 seconds (2 beeps will sound, display shows recirculation symbol), air recirculation will operate until button is pressed a second time to turn off. Prolonged recirculation may cause the windows to mist.

ACTUATOR MOTOR

There are 3 electric actuator motors that operate control flaps instead of manual control cables. Actuator motors operate blend air temperature control flap, air distribution control flap and recirculation flap. Actuator motors are controlled by the ATC ECU. Feedback potentiometers in actuator motors provide ATC ECU with flap position signals.

To control air distribution within cabin, ATC ECU signals actuator motor in heater assembly to move flaps to an appropriate position. In automatic and economy modes, if either driver's side and passenger's side temperature selection is set to LO and the other is set to a specific temperature, air distribution is set to face level. If one side is set to HI and one side is set to a specific temperature, air distribution is set to footwells only. If one side is set to LO and one side is set to HI, air distribution is set to face level and footwells.

When specific driver's side and passenger's side temperature selections are set, air distribution is determined from target air outlet temperatures. For higher target air outlet temperatures, air distribution is set to footwells only. For lower target air outlet temperatures, air distribution is set to face level only. For intermediate target air outlet temperatures, air distribution is set to face level and footwells. When air distribution is set to face level and footwells, ATC ECU varies the bias between footwells and face level outlets, in 3 stages, to provide a gradual transition of air distribution from footwells only to face level only. The 3 stages of bias are also employed when air distribution is manually selected to face level and footwells. During warm-up, air distribution changes to face level and footwells for a period, then reverts to footwells only. Period of air distribution at face level and footwells can be cancelled by pressing and holding A/C ON/OFF and defrost mode buttons, then turning ignition switch from off to on. Pressing and holding AUTO and defrost buttons, then turning ignition switch from off to on, restores period of air distribution at face level and footwells.

AMBIENT TEMPERATURE SENSOR

Ambient temperature sensor is an encapsulated thermistor that provides ATC ECU with external air temperature. Sensor is attached to cooling fan mounting bracket in front of condenser.

BLOWER CONTROL

ATC ECU operates a blower relay, power transistor and power relay to operate blower at one of 31 stepped speeds. All speed steps are available in automatic modes of blower control. In manual mode, speed steps 3, 10, 16, 22 and 31 are used to provide slow, three intermediate and fast blower speeds. ATC ECU energizes blower relay and modulates power transistor to operate blower for speed steps 1 to 30. For speed step 31, ATC ECU energizes power relay, which grounds blower motor, bypassing power transistor. In automatic, economy and defrost modes, blower speed is corrected for vehicle speed to compensate for increase in ram effect on inlet air as vehicle speed increases. Correction begins at approximately 31 MPH, when blower speed is progressively decreased as vehicle speed increases, until a maximum decrease of 13 steps at 76 MPH. Similarly, blower speed increases as vehicle speed decreases to approximately 31 MPH.

In automatic and economy modes, if driver's side and passenger's side temperature is set to LO or HI, blower operates at maximum speed with correction only for vehicle speed. If both driver's side and passenger's side outlet air temperatures are set to a specific temperature, blower speed corrections are added to compensate for heater coolant temperature, external air temperature, and solar load acting on vehicle

1. During warm-up, blower speed is set to step 3 when heater coolant temperature is less than approximately 68°F (20°C). From approximately 68°F (20°C), blower speed is progressively increased as coolant temperature increases, until maximum speed is set at approximately 122°F (50°C).
2. During cool down, blower speed is set to step 3, for 5 seconds after A/C system is turned on. Over the next 6 seconds, blower speed is progressively increased to maximum speed.
3. As cabin temperature increases to selected temperatures, blower speed is progressively reduced until, once selected temperatures have been reached, blower speed stabilizes at approximately step 6.
4. Solar heating correction is employed when air distribution is set to face level or to face and footwells. Correction progressively increases blower speed, up to a maximum of 9 steps, with increasing values of solar heating.

COMPRESSOR CONTROL

To engage compressor clutch, ATC ECU outputs a compressor clutch request to ECM, which then energizes A/C compressor clutch relay. Compressor operation is governed by evaporator outlet air temperature, at one of 2 settings, depending on amount of cooling required. When more cooling is required, compressor clutch request is output if evaporator outlet air temperature increases to 39°F (4°C) and cancelled when it decreases to 37°F (3°C). When less cooling is required, compressor clutch request is output if evaporator outlet air temperature increases to 52°F (11°C) and cancelled when it decreases to 50°F (10°C).

DUAL-PRESSURE SWITCH

Dual-pressure switch protects refrigerant system from extremes of pressure. The normally closed switch is located at top of receiver-drier. If minimum or maximum pressure limits are exceeded switch opens, disengaging compressor clutch. See SPECIFICATIONS . Minimum pressure limit protects compressor, by preventing operation of A/C system unless there is a minimum refrigerant pressure in system. Maximum pressure limit keeps refrigerant system within a safe operating pressure. Dual-pressure switch closes when system operating pressure changes to within limits.

EVAPORATOR TEMPERATURE SENSOR

Evaporator temperature sensor is an encapsulated thermistor that provides ATC ECU with evaporator air outlet temperature. Evaporator temperature sensor is installed in a clip located in evaporator core in heater assembly. ATC ECU uses input to prevent evaporator freeze-up.

FRONT THERMOSTATIC EXPANSION VALVE

Front thermostatic expansion valve meters flow of refrigerant into evaporator to match refrigerant flow with heat load of air passing through evaporator core. Thermostatic expansion valve is installed in heater assembly, in refrigerant inlet line to evaporator.

HEATER COOLANT TEMPERATURE SENSOR

Heater coolant temperature sensor is an encapsulated thermistor that provides ATC ECU with heater core coolant temperature. Sensor is located in heater assembly casing and presses against end tank of heater core.

IN-CAR TEMPERATURE SENSOR

In-car temperature sensor is an encapsulated thermistor that provides ATC ECU with cabin air temperature. Sensor is integrated into electric fan inlet, located behind grille in instrument panel, next to steering column. Fan runs continuously, while ignition is on, drawing air through grille and across sensor.

INLET AIR CONTROL

Inlet air source is automatically controlled while A/C system is off or on. While A/C system is on, inlet air source can also be manually controlled to give timed recirculated air or latched recirculated air. While A/C system is off, ATC ECU uses vehicle speed to determine inlet air source. With vehicle not moving, inlet air source is set to recirculated air. When vehicle speed is 17.5 mph or more, inlet air source changes to fresh air. Inlet air source then remains at fresh air until vehicle speed decreases to 5 mph, when it returns to recirculated air. While A/C system is on, ATC ECU uses driver's side and passenger's side temperature selections, vehicle speed, ambient air temperature and coolant temperature to determine inlet air source.

In automatic mode if one temperature selection is set to LO and one is set to a specific temperature or HI, inlet air is set to recirculated air. If one temperature selection is set to HI and one is set to a specific temperature or HI, inlet air is set to fresh air. When specific driver's side and passenger's side temperature selections are set, inlet air source remains at fresh air except when air distribution function is set to face level only or face level and footwell outlets. If air distribution function is set to face level only or face level and footwell outlets, at 56 MPH inlet air source changes to recirculated air (to exclude ram effect, which becomes excessive at speed). When vehicle speed decreases to 37.5 MPH, inlet air source returns to fresh air.

In defrost mode, inlet air source is set to fresh air except at low ambient air and coolant temperatures. If, within 5 minutes of ignition being turned on, vehicle speed is less than 5 MPH while external air temperature is 3°F (-16°C) or less and heater coolant temperature is 14°F (-10°C) or less, then inlet air source is automatically set to timed recirculated air mode. Timed recirculated air mode is cancelled immediately when vehicle speed reaches 5 MPH or more.

SUNLIGHT SENSOR

Sunlight sensor consists of 2 diodes that provide ATC ECU with light intensity sensed from left and right of vehicle. Inputs are used as a measure of solar heating effect on vehicle occupants. Sensor is located in center of dash upper surface.

Thermostatic Expansion Valve

Thermostatic expansion valve meters flow of refrigerant into rear evaporator to match heat load of air passing through evaporator core. A capillary tube, attached to outlet pipe of evaporator and connected to thermostatic expansion valve, automatically adjusts valve opening in relation to refrigerant temperature at evaporator outlet.

Blower

Rear blower controls volume of air being supplied to rear distribution outlets. Blower is an open hub, centrifugal fan powered by an electric motor. A dust filter is installed over fan inlet. Blower switch on control panel and resistor pack control 4 speeds of rear blower operation.

Resistor Pack

Rear resistor pack supplies reduced voltages to blower motor for blower speeds 1, 2 and 3. For blower speed 4, resistor pack is bypassed and battery voltage drives motor at full speed. Rear resistor pack is installed in air outlet from blower fan, so that any heat generated is dissipated by airflow.

Distribution System Air Ducts

Ducts connected to rear evaporator/blower motor assembly distribute air to 5 vent assemblies in roof.

Rear Control System

Rear control system operates rear blower to control operation of rear A/C. Control system consists of 2 control switches and a rear blower relay.

Control Switches

A rear A/C switch and a blower speed switch are installed on a control panel in roof lining. Rear A/C switch is a latching push switch with an Amber indicator lamp which illuminates when rear A/C is turned on. Blower speed switch is a slide switch with a positive detent at each of 4 speed positions (there is no off position).

Rear Blower Relay

Rear blower relay controls electrical supply to rear blower.

DEFAULT ATC ECU SETTINGS

If battery power supply to ATC ECU is disconnected, A/C control system reverts to default settings when battery power supply is restored. Default settings are

1. Temperature indications in Fahrenheit (in some markets a conversion connector is fitted to ATC ECU to change default temperature scale to Celsius).
2. Driver's side and passenger's side outlet temperatures of 72°F (22°C).
3. Audible warning is turned on.
4. Warm-up air distribution (to face level and footwells) function is turned on.
5. If A/C system is first turned on using A/C ON/OFF switch, automatic mode is engaged, regardless of settings in use when battery was disconnected.

COMPRESSOR OIL LEVEL

1. A certain amount of refrigerant oil must be removed from new replacement compressor before installing. To calculate amount of oil to be removed, remove drain plug from old compressor and gravity drain old oil into a calibrated measuring cylinder. Rotate compressor clutch to ensure compressor is completely drained.
2. Note amount of oil drained from old compressor. Remove drain plug from new replacement compressor and drain enough refrigerant oil to equal amount drained from old compressor plus 0.68 ounce of oil. Install and tighten compressor drain plug.

A/C SYSTEM PERFORMANCE

1. Place vehicle in a ventilated, shaded area free from excessive draft, with the doors and windows open. Ensure both surfaces of condenser are not restricted with dirt, leaves or other debris. Ensure evaporator condensate drain tubes are open and clear. Turn ignition on. Ensure blower is operating at low, medium and high speeds. Turn blower and ignition off.
2. Ensure tension of compressor driving belt is correct. Adjust as necessary. Inspect all A/C system connections for refrigerant oil. If oil is present, check for leaks, and repair as necessary. Start engine and allow to idle at normal operating temperature. Set temperature controls to cold. Turn A/C blower control on and off several times. Ensure that compressor clutch engages and releases each time.
3. Set temperature control to maximum cooling and blower control to high speed. Set engine speed to 1000 RPM. Check sight glass for bubbles or foam. Ensure sight glass is generally clear after 5 minutes of operation (occasional bubbles are okay). Repeat with engine speed set to 1800 RPM.
4. Gradually increase engine speed to 1800 RPM and check sight glass at intervals. Check for frosting on service valves. Check high pressure hoses and connections by hand for varying temperatures. Low temperature indicates a restriction or blockage at that point. Turn off A/C blower and stop engine.

A/C-HEATER UNIT